between legend and myth that has evolved with a people and their history, and that which is created by a single man just a few years ago.

Storytellers create new mythologies all the time, that's what Star Wars is all about, or the Star Trek Universe, or the worlds of Battlestar Galactica, the Terminator, Alien, King Arthur or even James Bond. Every movie franchise, novel cycle and video game universe is built around an alternate reality, a founding myth of some sort.

What makes Tolkien unique is the detail and depth of his mythology, and the exquisite craftsmanship and scholarship he has lavished on it.
Still, there are times when, in my opinion, he doesn't quite get it right; like Tom Bombadil.... He's the Middle Earth equivalent of Jar-Jar Binks.